1. Field of the Invention
This invention relates generally to refrigerator systems for transportable vehicles, and more particularly to a method and apparatus for utilizing carbon dioxide in a chamber in trucks, rail cars and the like for transporting frozen food without mechanical refrigeration units.
2. Description of the Prior Art
Refrigeration systems for railroad cars and trucks have typically utilized mechanical refrigeration units. In such mechanical refrigeration units it is always of great concern that the units are operational and would not breakdown. The cost of maintenance, both in time and dollars, is often substantial. In addition, over a long haul, it is necessary to frequently check the mechanical refrigeration system to make certain that they are still operational. Further, the mechanical works and fuel add to the overall weight of the rail car.
Non-mechanical refrigeration units have been proposed, but they have been mainly suitable only for trucks. One such non-mechanical refrigeration system is disclosed in U.S. Pat. No. 3,561,266 and was issued to Julius Rubin on Feb. 9, 1971. This non-mechanical refrigeration system utilized liquid CO.sub.2 that is converted into solid dry ice, often referred to as snow. Liquid CO.sub.2 is injected into one end of a cold plate container at the time refrigeration is desired in a given chamber. The liquid CO.sub.2 is converted to snow and CO.sub.2 vapor. The cold plate would act as a source of refrigeration for the truck. While the Rubin patent does disclose that such a CO.sub.2 cold plate system could be used for railroad cars, such a system has never proved practical.
Another example of a CO.sub.2 charged cooling unit is disclosed in U.S. Pat. No. 4,248,060 issued to Paul Franklin, Jr. on Feb. 3, 1981. The Franklin patent discloses a cooling cabinet utilizing CO.sub.2 snow and having associated therewith a passageway structure for pumping air to provide for cooling in the area surrounding the cooling unit.
In both of the above noted prior arts units, the CO.sub.2 snow was directly used as the refrigerant for the cooling chamber. The vapor of the CO.sub.2 snow as it evaporates was typically vented to the outside and not used directly used as the source of cooling.
The present invention addresses the problems of the prior art refrigeration systems.